Change dont_embed_build_metadata default to 1 except for Official build and fix some unittests.

base/build_time.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_BUILD_TIME_
 #define BASE_BUILD_TIME_
 
 #include "base/base_export.h"
 #include "base/time/time.h"
 
 namespace base {
 
 // GetBuildTime returns the time at which the current binary was built.
 //
 // This uses the __DATE__ and __TIME__ macros, which don't trigger a rebuild
 // when they change. However, official builds will always be rebuilt from
 // scratch.
 //
 // Also, since __TIME__ doesn't include a timezone, this value should only be
 // considered accurate to a day.
+//
+// NOTE: This function is disabled except for the official builds, by default
+// the date returned is "Sep 02 2008 08:00:00 PST".
 Time BASE_EXPORT GetBuildTime();
 
 }  // namespace base
 
 #endif  // BASE_BUILD_TIME_